# Boost converter for PV applications

I am designing a 18V to 24V boost converter with a solar panel as its input and a variable resistor at the load side for taking measurements. The boost converter will be doing the Maximum Power Point Tracking (MPPT) for the panel. However I am confused about one thing - how will I keep the output constant at around 24 V regardless of the irradiation falling on the panel?

Also is it possible to do MPPT AND keep the output of the converter constant using just a single boost converter?

The solar panel has the following specifications: Pmax = 50 Watts, Vmp = 18.68 V, Imp = 2.77 A, Voc = 22.53 V, Isc = 2.97 A

• What would the laws of thermodynamics say about your situation you’re describing? Feb 24, 2018 at 19:31

You are confused about a lot of things.

MPPT is only useful when the load can accept the maximum power. This usually happens with solar battery chargers and grid-tie inverters. But if the load does not need the maximum power that the panel can produce, then you don't want to run MPPT. In that case, you want to select the duty cycle that produces the correct output voltage, regardless of the maximum power point.

Also, if the solar panel is not able to supply the power needed by the load (for example when the sun is going down or if the sun is obscured by clouds) then there is no way to maintain the output voltage that the load needs. You will have to shut down the load, or run the load at reduced voltage.

I think what you want is just a boost controller with a fixed output voltage, not an MPPT controller. If a cloud goes in front of the sun, or when the sun goes down, then you need to make sure your system handles this gracefully. Maybe you could have a small micronctroller that detects when this happens, and shuts down the load, then attempts to restart once every minute or once every hour, or whatever seems reasonable. It is not easy to say what is best without full knowledge of what you are trying to do.

The algorithm for an MPPT battery charger is just to try different PWM duty cycles in order to maximize battery charge current. You also need to monitor battery voltage and possibly battery temperature to avoid over-charge. There is more to it to have a safe system. That is just an outline.

• I think I get what you mean. When the irradiation changes, the power will change and therefore the voltage level cannot stay constant. What I am trying to do is MPPT with a variable resistor as the load to show that no matter what resistance value I set, the power extracted is the MPP for a particular irradiation. However if I want to maintain the output voltage at a constant level I would have to use a regulator or another converter is that correct? Feb 27, 2018 at 19:38
• Why do you want to do an MPPT with a variable resistor? For purposes of demonstration? I think it is possible to get a variable power resistor. Feb 28, 2018 at 6:34

Just think about what you're asking. You want PV MPPT so that means that your output power is variable (but maximum for any given solar input, it'll be variable anyway).

You also say that you want output constant at around 24V.

So you have variable output power with fixed output voltage. This means you must have variable output current and you can't dictate the output with a variable resistor.